1. Field of the Invention
The present invention relates to improvements in a transfer device including an intermediate transfer belt provided to extend in an arrangement direction of a plurality of photosensitive drums, and primary transfer rollers each transferring a toner image formed on a corresponding one of the photosensitive drums onto the intermediate transfer belt and an image forming apparatus including the transfer device.
2. Description of Related Art
Conventionally known is an image forming apparatus which has a structure including a transfer device provided with an intermediate transfer belt being driven in a state suspended in an arrangement direction of a plurality of photosensitive drums, and primary transfer rollers each transferring a toner image formed on a corresponding one of the photosensitive drums onto the intermediate transfer belt.
Each of the primary transfer rollers is moved away from and closer to the intermediate transfer belt between a position causing the intermediate transfer belt to be in contact with the photosensitive drums, and a position causing the intermediate transfer belt to be separated from the photosensitive drums (for reference, see Japanese Patent Application Publication No. 2003-186313).
Moreover, among the transfer devices, there is the one in which the center distance between the center axes of the photosensitive drum and the primary transfer roller at the position causing the intermediate transfer belt to be in contact with the photosensitive drums is set to be larger than the sum of the radiuses of the photosensitive drum of the primary transfer roller. The transfer device of this type is so-called an offset type transfer device.
In the meantime, a transfer device of this offset type has a configuration in which the position of the primary transfer rollers is changed between the position causing the intermediate transfer belt to be in contact with the photosensitive drums and the position causing the intermediate transfer belt to be separated from the photosensitive drums. Thus, a non-contacting distance of the intermediate transfer belt varies every time the position of the intermediate transfer belt is changed. Here, the non-contacting distance denotes a distance between a contacting portion at which the intermediate transfer belt is in contact with each of the photosensitive drums, and a contacting portion at which the intermediate transfer belt is in contact with a corresponding one of the primary transfer roller.
As a result, there is a problem that the power distribution resistance from the photosensitive drum to the primary transfer roller changes, and toner transfer efficiency varies.